The present invention relates to probes for use as sensors to detect selective ionic characteristics in a liquid solution and more particularly to a probe for use in detecting the oxidation and/or reduction potential of ions in such a solution.
In the past it has been common to construct probes using glass housings. With probes designed to detect the oxidation reduction potential of a solution (referred to as ORP probes), and electrode was formed using a platinum band bonded to a glass tube. Platinum was used because of its desirable conductivity characterstics and because of its resistance to various chemicals i.e. such as to HF, hydrofluoric acid. The platinum band typically was bonded to the glass tube during firing. Thus a straight hollow glass tube was fired to provide a necked down portion on which the platinum band was secured during the firing step. The result was a good, fluid tight bond. The platinum band was connected to a lead wire of platinum which was fed through an opening in the neck of the hollow galss tube for connection to a meter. At some location the platinum wire was connected by spot welding to a silver wire which completed the electrical circuit to the meter. Because of the heat generated in firing the glass tube to form the necked down portion the welded connection to the silver wire was located a considerable distance from the platinum band. This inherently required a substantial length of expensive platinum wire. At the same time the glass probe was susceptible to breakage in shipment and in use and hence was not adapted for rugged use or handling. Also the glass housing construction provided a reduced life for the electrode when used in solutions such as hydrofluoric acid and (HF) which attack and/or dissolve glass.
In the present invention as epoxy type plastic tube is used in place of the glass tube in a construction which obviates the problems of the prior construction and results in a rugged less expensive construction.